Gram-positive microorganisms cause the majority of systemic infections. One important member of these Gram-positive pathogens is Staphylococcus aureus (S. aureus). About 20% of the population is a long-term carrier of S. aureus. S. aureus can cause a range of illnesses from minor skin infections, such as pimples, impetigo (may also be caused by Streptococcus pyogenes), boils, cellulitis folliculitis, furuncles, carbuncles, scalded skin syndrome and abscesses, to life-threatening diseases such as pneumonia, meningitis, osteomyelitis, endocarditis, Toxic shock syndrome (TSS), and septicemia. S. aureus is capable of infecting all kinds of organs and tissues. S. aureus infections occur in immunocompetent as well as immune compromised people. About 50% of the infections in US intensive care units are caused by this pathogen. Three hundred thousand S. aureus infections per year, resulting in 12,000 deaths, are reported in the US (see also Moran et al. NEMJ 355, 666-674 (2006)).
A major problem is the increasing antibiotic resistance of S. aureus. Methicillin-resistant S. aureus (MRSA) emerged in the 1960s. It was initially identified in health care settings. However, MRSA appears to be present among persons in the community which have not been hospitalized. Treatment of MRSA is difficult and expensive, due to the limited sensitivity of MRSA to antibiotics. However, very few alternatives of antibiotics are available. Vancomycin is often used to treat penicillin-resistant MRSA. U.S. Pat. No. 6,939,543 describes a murine antibody against lipoteichoic acid (LTA) which is capable of binding S. aureus. Based on this murine antibody, a recombinant chimeric mouse/human antibody was produced which contains human heavy and light chain constant domains. However, such chimeric mouse/human antibody has the disadvantage that murine sequences are present, which involves the risk of serious side effects when administered to humans.